[K03NT3S31N]

https://priorityunlock.com/

This is a SIM unlocker, for phones that come branded with a certain carrier and can't be used with any other, it doesn't remove the blacklist

Good to know anyways. Have you tried it before?

[mothered]

Argos delivered the phone the day after, the seals on the phone were a bit funky looking anyway, I opened the seal with a hair dryer and got it very hot, replaced phone with blacklisted one and it got picked up the same day.

The refund is now in my bank account and I have not heard anything from Argos, so I would mark this as a successful SE.

Given the funds have cleared Into your account, the claim Is finalized therefore the SE has certainly succeeded.

Well done.

I have reported my bank card as lost in case they try to recharge it, I’m not sure if it helps against that but just a precaution.

Good move.

Even If the card wasn't cancelled, when your return Is sold, It will go through so many hands, hence It'll be extremely difficult (If not Impossible) to pinpoint the Inconsistency to you.

[Nabeshin]

https://priorityunlock.com/

This is a SIM unlocker, for phones that come branded with a certain carrier and can't be used with any other, it doesn't remove the blacklist

Good to know anyways. Have you tried it before?

No, since all phones are sold sim-unlocked here, that's mostly a US  thing, maybe even UK?